MONTPELIER — Republican Randy Brock, the Vermont GOP’s nominee for governor in 2012, announced in an email Sunday that he will not challenge Democratic Gov. Peter Shumlin again this year.

Brock, a former state auditor and state senator, had been publicly mulling a run. His decision comes after Stowe Rep. Heidi Scheuermann and former Wall Street executive Bruce Lisman already bowed out this year.

Scott Milne, president of Milne Travel, is the only other known Republican considering a run. Milne has said he wants a primary, however.

“I will not be a candidate for Governor of Vermont in 2014,” Brock wrote in his email. “This decision has not been easy to reach. I have arrived at it over several months after careful thought, much input and serious deliberation.”

Brock lost the 2012 race to Shumlin after winning only 38 percent of the vote after putting about $300,000 of his own money into the campaign. Brock said he was not prepared to pump his own cash into a race this year.

He said he is opting out of challenging Shumlin again this year despite persistent urging to do so from supporters.

“I am thankful to the many Vermonters who have called upon me to run. I have heard from people from all over our state offering words of encouragement,” he wrote. “This outpouring of support from so many has been extremely heartening and I will always be grateful for their unwavering loyalty.”

Brock, noting that his name will not appear on a ballot for the first time in 10 years, said he will miss being out on the campaign trail. But, sitting the election out “is the right decision for me and my family,” he said.

He pledged to remain “involved in helping to shape public policy.” The former auditor also said he plans “to continue to contribute to the debate through critical analysis and commentary.”